Showing papers on "Vanadate published in 1995"
TL;DR: The finding that vanadate trapping of nucleotide at just one site/Pgp is sufficient to give full inhibition of ATPase activity shows that the two predicted nucleotide sites can not function independently as catalytic sites.
365 citations
TL;DR: The P-type ATPase, CopB, of E. hirae is required for the copper resistance displayed by this organism and thus was postulated to be a copper pump.
286 citations
TL;DR: The results suggest that Ca2+ regulates the activity of plasma membrane H+-ATPases in higher plant cells, thereby modulating stomatal movement and other cellular processes in plants.
Abstract: Opening of the stomata is driven by the light-activated plasma membrane proton pumping ATPase, although the activation and inactivation mechanism of the enzyme is not known. In this study, we show that the H+-ATPase in guard cells is reversibly inhibited by Ca2+ at physiological concentrations. Isolated microsomal membranes of guard cell protoplasts from fava bean exhibited vanadate-sensitive, ATP-dependent proton pumping. The activity was inhibited almost completely by 1 [mu]M Ca2+ with a half-inhibitory concentration at 0.3 [mu]M and was restored immediately by the addition of 1,2-bis(2-aminophenoxy)ethane N,N,N[prime],N[prime]-tetraacetic acid, a calcium chelating reagent. Similar reversible inhibition by Ca2+ was shown by the generation of electrical potential in the membranes. Activity of ATP hydrolysis was inhibited similarly by Ca2+ in the same membrane preparations. The addition of 1,2-bis(2-aminophenoxy)ethane N,N,N[prime],N[prime]-tetraacetic acid and EGTA, Ca2+ chelators, to epidermal peels of fava bean induced stomatal opening in the dark, and the opening was suppressed by vanadate. This suggests that the lowered cytosolic Ca2+ activated the proton pump in vivo and that the activated pump elicited stomatal opening. Inhibition of H+-ATPase by Ca2+ may depolarize the membrane potential and could be a key step in the process of stomatal closing through activation of the anion channels. Furthermore, similar inhibition of the proton pumping and ATP hydrolysis by Ca2+ was found in isolated plasma membranes of mesophyll cells of fava bean. These results suggest that Ca2+ regulates the activity of plasma membrane H+-ATPases in higher plant cells, thereby modulating stomatal movement and other cellular processes in plants.
255 citations
TL;DR: The inhibited P-glycoprotein·Mg-nucleotide·vanadate complex is probably an analog of the catalytic transition state, implying that when one nucleotide site assumes the catalytical transition state conformation the other site cannot do so and suggesting that the two sites may alternate in catalysis.
224 citations
TL;DR: Disruption of both PDR5 and SNQ2 in a pdr1 mutant decreases the cell growth rate and reveals the presence of at least two other ATP binding cassette proteins in the 160-kDa overexpressed band that have been identified by amino-terminal microsequencing.
162 citations
TL;DR: The normalization of both serum glucose and FFA levels by vanadyl ion was concluded to be due to the incorporation of van adyl ion into the adipocytes, in which the metal ion acts on the glucose transporter and induces both the promotion of glucose uptake and the decrease of FFA release form peripheral adipocytes.
Abstract: When rats with streptozotocin (STZ)-induced diabetes were given a daily intraperitoneal (i. p.) injection of VOSO4 (+4 oxidation state of vanadium), their serum glucose dropped from hyperglycemic level to normal level within 2 d and serum free fatty acid (FFA) level also dropped to normal level. Vanadium was incorporated in most organs as well as in the adipose tissues, as detected by neutron activation analysis (NAA). The mechanism for the insulin-like action of vanadium in terms of FFA release from isolated rat adipocytes was investigated : (1) Vanadyl (IV) and vanadic (III) ions normalize the FFA release in the adipocytes treated with epinephrine ; (2) vanadate (V) ion treated with ascorbic acid, cysteine or glucose is effective in normalizing the FFA release but vanadate ion alone has no effect on FFA release ; (3) vanadyl ion is incorporated into the adipocytes, while vanadate ion is not, as indicated by ESR spectroscopy ; and (4) vanadyl ion can act on the glucose transporter, as indicated by experiments using cytochalasin B which is an inhibitor of this transporter. From these results, the normalization of both serum glucose and FFA levels by vanadyl ion was concluded to be due to the incorporation of vanadyl ion into the adipocytes, in which the metal ion acts on the glucose transporter and induces both the promotion of glucose uptake and the decrease of FFA release from peripheral adipocytes. The vanadyl state was suggested to be a possible pharmacologically active form of vanadium allowing the insulin-like action. We further propose that the monitoring of serum FFA level is another sensitive index in addition to serum glucose level by which to know the degree of the diabetes, and the FFA release from adipocytes is a good in vitro evaluation system to find a compound which shows an insulin-like action.
154 citations
TL;DR: The results suggest that vanadium derivatives behave like growth factors on osteoblast-like cells and are potential pharmacological tools in the control of cell growth.
Abstract: The effect of different vanadium compounds on proliferation and differentiation was examined in osteoblast-like UMR106 cells. Vanadate increased the cell growth in a biphasic manner, the higher doses inhibiting cell progression. Vanadyl stimulated cell proliferation in a dose-responsive manner. Similar to vanadate, pervanadate increased osteoblast-like cell proliferation in a biphasic manner but no inhibition of growth was observed. Vanadyl and pervanadate were stronger stimulators of cell growth than vanadate. Only vanadate was able to regulate the cell differentiation as measured by cell alkaline phosphatase activity. These results suggest that vanadium derivatives behave like growth factors on osteoblast-like cells and are potential pharmacological tools in the control of cell growth.
110 citations
TL;DR: It is argued that several Ca2+- and pH-related processes are pivotal for tip growth in root hairs: with respect to Ca2+, these are an inwardly directed Ca1+-current, localized elevated cytosolic [Ca2+] in the tip, and constant Ca2-circulation.
Abstract: SUMMARY
In Sinapis root hair cells, tip growth has been measured and studied with different electrophysiological techniques. Applying ion-selective microelectrodes, we measured 452–776 nM free [Ca2+] in the tip, which is about three times the concentration found in the base. The cytosolic pH of 7.1–7.3 in the tip is statistically not different from values measured in the base. The cells react to changes in external [Ca2+] between 0.01 and 10 mM with transient changes in growth intensity and cytosolic [Ca2+]: increased external [Ca2+] elevates cytosolic [Ca2+] followed by a growth burst. Whereas external [Ca2+] lower than 1 μM is inhibitory to steady state tip growth, concentrations up to 30 mM are not. Vibrating probe analysis reveals inwardly directed net Ca2+-currents in the tip only. The calcium channel antagonists nifedipine and La3+ decrease cytosolic free [Ca2+], inhibit the inwardly directed Ca2+-current and tip growth. Dibromo-BAPTA, injected into the cells, also decreases cytosolic [Ca2+] and inhibits growth, but only marginally depolarizes the cells. Abrupt changes in external pH between 5 and 9 affect cytosolic pH and transiently inhibit tip growth, regardless of the direction of the pH-shift. Acetic acid and NH4Cl both inhibit tip growth only, when the cytosolic pH is shifted from its steady state value. Tip growth is inhibited in the presence of the ATPase inhibitors DCCD, vanadate and erythrosin B. We argue that several Ca2+- and pH-related processes are pivotal for tip growth in root hairs: with respect to Ca2+, these are an inwardly directed Ca2+-current, localized elevated cytosolic [Ca2+] in the tip, and constant Ca2+-circulation. For pH, an active H+-pump and a tightly regulated cytosolic pH at the tip appear important, however not an internal pH-gradient.
106 citations
TL;DR: It has been shown that coadministration of vanadate and TIRON, an effective chelator in the treatment of vanadium intoxication, reduced the tissue accumulation of this element, decreasing the possibility of toxic side effects derived from chronic vanadium administration without diminishing the hypoglycemic effect ofVanadium.
Abstract: The possible use of vanadium compounds in the treatment of diabetic patients is now being evaluated. However, previously to establish the optimal maximum dose for diabetes therapy, it should be taken into account that vanadium is a highly toxic element to man and animals. The toxic effects of vanadium are here reviewed. The tissue vanadium accumulation, which would mean an additional risk of toxicity following prolonged vanadium administration is also discussed. Recently, it has been shown that coadministration of vanadate and TIRON, an effective chelator in the treatment of vanadium intoxication, reduced the tissue accumulation of this element, decreasing the possibility of toxic side effects derived from chronic vanadium administration without diminishing the hypoglycemic effect of vanadium. However, previously to assess the effectiveness of this treatment in diabetic patients, a critical reevaluation of the antidiabetic action of vanadium and its potential toxicity is clearly needed.
97 citations
TL;DR: It is shown that administration of vanadate or selenate to streptozotocin-induced diabetic rats not only normalizes blood glucose levels similarly to insulin but also positively affects the expression of two key metabolic enzymes, glucose-6-phosphate dehydrogenase (G6PDH) and fatty acid synthase (FAS).
84 citations
TL;DR: It is concluded that three properties, stability, lability and redox chemistry are critical to prolong the half-life of the insulin-mimetic form of vanadium compounds under physiological conditions and should all be considered in development ofVanadium-based oral insulin- mimetic agents.
Abstract: The stability of 11 vanadium compounds is tested under physiological conditions and in administration fluids. Several compounds including those currently used as insulin-mimetic agents in animal and human studies are stable upon dissolution in distilled water but lack such stability in distilled water at pH 7. Complex lability may result in decomposition at neutral pH and thus may compromise the effectiveness of these compounds as therapeutic agents; Even well characterized vanadium compounds are surprisingly labile. Sufficiently stable complexes such as the VEDTA complex will only slowly reduce, however, none of the vanadium compounds currently used as insulin-mimetic agents show the high stability of the VEDTA complex. Both the bis(maltolato)oxovanadium(IV) and peroxovanadium complexes extend the insulin-mimetic action of vanadate in reducing cellular environments probably by increased lifetimes under physiological conditions and/or by decomposing to other insulin mimetic compounds. For example, treatment with two equivalents of glutathione or other thiols the (dipicolinato)peroxovanadate(V) forms (dipicolinato)oxovanadate(V) and vanadate, which are both insulin-mimetic vanadium(V) compounds and can continue to act. The reactivity of vanadate under physiological conditions effects a multitude of biological responses. Other vanadium complexes may mimic insulin but not induce similar responses if the vanadate formation is blocked or reduced. We conclude that three properties, stability, lability and redox chemistry are critical to prolong the half-life of the insulin-mimetic form of vanadium compounds under physiological conditions and should all be considered in development of vanadium-based oral insulin-mimetic agents.
TL;DR: Pertungstate and permolybdate were found to stimulate all or most of the insulin bioeffects in rat adipocytes and are 80-180-fold more potent stimulators than the corresponding metallooxides.
Abstract: In previous studies, tungstate and molybdate were found to mimic the biological actions of insulin. It was suggested that these metallooxides initially inhibit vanadate-sensitive protein phosphotyrosine phosphatase (PTPase). This, in turn, stimulates a staurosporine-sensitive cytosolic protein tyrosine kinase (cytPTK), which activates several insulin bioeffects via insulin-independent pathways (Shisheva & Shechter, 1991, 1993; Elberg et al., 1994). Tungstate and molybdate, however, facilitate bioeffects in rat adipocytes only at high (millimolar) concentrations (Goto et al., 1992). We report here that incubations of tungstate or molybdate with hydrogen peroxide (H2O2) result in the formation of pertungstate (pW, peroxide of tungstate) or permolybdate (pMo, peroxide of molybdate). Pertungstate and permolybdate were found to stimulate all or most of the insulin bioeffects in rat adipocytes. Moreover, these permetallooxides are 80-180-fold more potent stimulators than the corresponding metallooxides. This shift in potency resembles that of pervanadate relative to vanadate in stimulating the same effect in rat adipocytes (Fantus et al., 1989). pW and pMo are also active in normalizing blood glucose levels in streptozotocin-induced diabetic rats. Further studies aimed at understanding the higher efficacy of this permetallooxide revealed the following: (a) All three permetallooxides (pV, pW, pMo) are oxidizing agents relative to reduced glutathione (GSH). They oxidize stoichiometric amounts of GSH to GSSG. (b) All three metallooxides do not oxidize GSH to GSSG. (c) Both metallooxides and permetallooxides inhibit rat adipocytic PTPase at micromolar quantities (IC50 = 3-10 microM). Permetallooxides, however, inhibited a larger PTPase fraction (80-100%) compared to metallooxides (40-70% of the total).(ABSTRACT TRUNCATED AT 250 WORDS)
Journal Article•
TL;DR: Detailed studies ofVanadate-initiated inhibition of enzymes will expand the understanding of the various mechanisms of action of vanadate and its derivatives that have been briefly described here and will doubtless provide insight into other functions of this unique material.
Abstract: The chemical similarities between vanadate and phosphate combined with the ability of vanadate to readily undergo changes in coordination geometry allows this ion to strongly influence the function of a large variety of phosphate-metabolizing enzymes. As transition state analogs, spontaneously formed vanadate complexes are potent inhibitors of a number of enzymes, including some ribonucleases, mutases, and phosphatases. In addition, vanadate is an effective inhibitor of many ATPases, kinases, lyases, and synthases. Vanadate oligomers tend to be weaker inhibitors than vanadate but do influence the function of dehydrogenases, mutases, aldolases, kinases, and others. Of the oligomers, decavanadate is unique in that it seems to bind only in polyphosphate binding domains. Peroxovanadate has not yet been well studied but it seems to inhibit enzymes that do not utilize a pentacoordinate vanadate in the catalysis cycle. Additional detailed studies of vanadate-initiated inhibition of enzymes will expand our understanding of the various mechanisms of action of vanadate and its derivatives that have been briefly described here and will doubtless provide insight into other functions of this unique material.
TL;DR: The phenotypes of these vanadate-resistant mutants are consistent with an alteration in the permeability or specificity of the Golgi apparatus.
Abstract: Orthovanadate is a small toxic molecule that competes with the biologically important oxyanion orthophosphate. Orthovanadate resistance arises spontaneously in Saccharomyces cerevisiae haploid cells by mutation in a number of genes. Mutations selected at 3 nM sodium orthovanadate have different degrees of vanadate resistance, hygromycin sensitivity, detergent sensitivity and sporulation defects. Recessive vanadate-resistant mutants belong to at least six genetic loci. Most mutants are defective in outer chain glycosylation of secreted invertase (van1, van2, van4, van5, van6, VAN7-116 and others), a phenotype found in some MNN or VRG mutants. The phenotypes of these vanadate-resistant mutants are consistent with an alteration in the permeability or specificity of the Golgi apparatus. The previously published VAN1 gene product has a 200 amino acid domain with 40% identity with the MNN9 gene product and 70% identity with the ANP1 gene product. Cells containing the van1-18, mnn9 (vrg6) or anp1 mutations have some phenotypic similarities. The VAN2 gene was isolated and its coding region is identified and reported. It is an essential gene on chromosome XV and its translated amino acid sequence predicts a unique 337 amino acid protein with multiple transmembrane domains.
TL;DR: It is observed that vanadate vanadyl, when added to intact rat adipocytes, mimics the biological actions of insulin in stimulating hexose uptake and glucose oxidation and initiated a long, currently active, field of research among basic scientists and diabetologists.
Abstract: Most or all mammalian cells contain vanadium at a concentration of 0.1–1.0 μM. The bulk of the vanadium in cells is probably in the reduced vanadyl (IV) form. Although this element is essential and should be present in the diet in minute quantities, no known physiological role for vanadium has been found thus far. In the years 1975–1980 the vanadate ion was shown to act as an efficient inhibitor of Na+,K+-ATPase and of other related phosphohydrolyzes as well. In 1980 it was observed that vanadate vanadyl, when added to intact rat adipocytes, mimics the biological actions of insulin in stimulating hexose uptake and glucose oxidation. This initiated a long, currently active, field of research among basic scientists and diabetologists. Several of the aspects studied are reviewed here.
TL;DR: In this article, the electron paramagnetic resonance (EPR) spectra of binary vanadium tellurite (V2O5TeO2) and vanadium phosphate glasses have been taken, which are typical of V4+ ions present in vanadyl (VO2+) form in the glass.
Abstract: Electron paramagnetic resonance (EPR) spectra of binary vanadium tellurite (V2O5TeO2) and vanadium phosphate (V2O5P2O5) glasses have been taken. The spectra are typical of V4+ ions present in vanadyl (VO2+) form in the glass. Well resolved spectra are observed only for glasses having ⩽ 30 mol% V2O5. In order to obtain resolved spectra, glasses with higher concentration of V2O5 are annealed in oxygen. Concentration of V4+ ions in annealed and unannealed samples has been calculated by using EPR spectra. Critical concentrations of V4+ ions below which the spectra are resolved are reported for different compositions of the glass.
TL;DR: Gutheil et al. as mentioned in this paper showed that exposure of cells to the intracellular Ca2+ pump blocker, thapsigargin (TG), results in emptying of Ca 2+ pools and termination of cell proliferation.
TL;DR: The origin of the oxygen atoms in the dioxygen produced by the V-BrPO-catalyzed bromide-assisted disproportionation of hydrogen peroxide has been shown through H2(18)O2 labeling experiments to originate from the same molecule of hydrogenperoxide.
Abstract: Hydrogen peroxide, which is a substrate of vanadium bromoperoxidase (V-BrPO), has been shown to be a noncompetitive inhibitor of V-BrPO. Hydrogen peroxide inhibition increases with increasing pH. The inhibition is reversible under the conditions of the initial steady-state kinetic experiments. Analysis of the inhibition constants (KiiH2O2, KisH2O2) versus H+ concentration indicates that an ionizable group with a pKa between 6.5 and 7 is involved in the inhibition. The origin of the oxygen atoms in the dioxygen produced by the V-BrPO-catalyzed bromide-assisted disproportionation of hydrogen peroxide has been shown through H2(18)O2 labeling experiments to originate from the same molecule of hydrogen peroxide. V-BrPO-catalyzed bromination is shown to be an electrophilic (Br+) as opposed to a radical (Br.) process. The stoichiometry of H2O2 consumed to MCD reacted or to O2 produced is reported. The concentration of hydrogen peroxide also affects the competition of dioxygen formation during MCD bromination; competitive dioxygen formation is strongly enhanced at high pH. Turnover of V-BrPO under conditions of very high hydrogen peroxide concentration leads to irreversible inactivation at pH 4 and pH 5. Much less inactivation occurs during turnover at long reaction times at higher pH (> pH 6), and the inactivation can be fully reversed by subsequent addition of vanadate.
TL;DR: In this paper, an intercalated vanadyl vanadate has been synthesized from a mixture of V2O5, SiO2, HF, 1,3-diaminopropane, and H2O in the ratio 1:2.2:2:0.6:80.
TL;DR: It is concluded that the use of the above-mentioned protein tyrosine kinase inhibitors in the rat aorta blocks a step involved in Ca2+ entry and Ca2- store refilling.
TL;DR: It is demonstrated that although vanadate is able to stimulate glucose transport in insulin-resistant muscle, it is not able to normalize transport to the same rate achieved in diabetes-sensitive muscle.
Abstract: In response to insulin, several proteins are phosphorylated on tyrosine and on serine/threonine residues. Decreased phosphorylation of signaling peptides by a defective insulin receptor kinase may be a cause of insulin resistance. Accordingly, inhibition of the appropriate phosphatases might increase the phosphorylation state of these signaling peptides and thereby elicit increased glucose transport. The purpose of this study was to examine the effect of the serine/threonine phosphatase inhibitor okadaic acid and the tyrosine phosphatase inhibitors phenylarsine oxide and vanadate on 2-deoxyglucose transport in insulin-resistant human skeletal muscle. All three phosphatase inhibitors stimulated 2-deoxyglucose transport in insulin-resistant skeletal muscle. These data suggest that these compounds have bypassed a defect in at least one of the signaling pathways leading to glucose transport. Furthermore, maximal transport rates induced by the simultaneous presence of insulin and phosphatase inhibitor in insulin-resistant muscle were equal to insulin-stimulated rates in lean control subjects. However, both vanadate alone and vanadate plus insulin stimulated 2-deoxyglucose transport significantly more in insulin-sensitive tissue than in insulin-resistant tissue. These results demonstrate that although vanadate is able to stimulate glucose transport in insulin-resistant muscle, it is not able to normalize transport to the same rate achieved in insulin-sensitive muscle.
TL;DR: In this paper, Mexican V2O6·2H2O vanadates, where MeCu, Co, Zn, Mn, Co and Ni vanadate were found to be reversible to lithium intercalation at average voltages from 1.3 to 1.9 V (versus Li) and their specific capacities were dependent on annealing temperature.
TL;DR: In this paper, the structure of lead vanadate glasses, x PbO · (100 - x )V 2 O 5 (x = 55, 50, 40, 30), has been investigated by means of infrared and 51 V static and magic angle spinning nuclear magnetic resonance (MAS-NMR) and 207 Pb MAS-NMRI spectroscopies.
Abstract: The structure of lead vanadate glasses, x PbO · (100 - x )V 2 O 5 ( x = 55, 50, 40, 30) has been investigated by means of infrared and 51 V static and magic angle spinning nuclear magnetic resonance (MAS-NMR) and 207 Pb MAS-NMR spectroscopies. The 51 V NMR spectral parameters of various constituent vanadate groups in lead vanadate glasses were determined by spectrum simulation on the basis of our previous results on alkaline earth vanadate glasses. The structure of 55PbO · 45V 2 O 5 glass mainly consists of VO 4 tetrahedra, which are composed of V 2 O 7 4− and (VO 3 ) n single chains. The structure of x PbO · (100 - x )V 2 O 5 glasses ( x = 30, 40, 50) consists of both VO 4 tetrahedra and VO 5 trigonal bipyramids. These VO n polyhedra ( n = 4, 5) compose at least four types of vanadate group, i.e., V 2 O 7 4− (VO 3 ) n single chains, branched VO 4 group and (V 2 O 8 ) n zigzag chains depending on the PbO content.
TL;DR: Observations indicate that cell surface fluorescence was due to the capture of Ca2+ by Calcium Green C18 after Ca2-ATPase had been translocated across osteoblast plasma membranes.
TL;DR: The results indicate that an interaction between palytoxin and Na, K-ATPase leads to opening of a 10-pS ion channel, and raise the possibility that a channel structure may exist in the sodium pump which is uncovered by the action of palyToxin.
Abstract: The effects of ouabain, ATP, and vanadate on palytoxin induction of ion channels were examined with the aim of elucidating the role of Na,K-ATPase in palytoxin action. Palytoxin-induced membrane depolarization of crayfish giant axons and single channel currents of frog erythrocytes and mouse neuroblastoma N1E-115 cells were examined using the intracellular microelectrode and patch-clamp techniques. External application of palytoxin in nanomolar concentrations induced depolarization in the crayfish giant axons, and the depolarization was inhibited by pretreatment of the axon with ouabain (10 μM). Internally perfused axons were less sensitive to palytoxin unless ATP (6 mM) was added internally. In patch-clamp experiments, picomolar palytoxin in the patch electrode induced single channels in both cell-attached and inside-out patches of erythrocytes and neuroblastoma cells. The induced channels had a conductance of about 10 pS, reversed near 0 mV in physiological saline solution, and was permeable to Na+, K+, Cs+, and NHinf4sup+, but not to choline. Single channel activities induced by palytoxin were inhibited by ouabain (10 μM) and vanadate (1 mM), but promoted by ATP (1 mM). The modulating effects of ouabain, vanadate, and ATP on palytoxin action suggest that the Na,K-ATPase is involved in the induction of single channels by palytoxin. Palytoxin-induced and ouabain-inhibitable single channels were observed in planar lipid bilayer incorporated with purified Na,K-ATPase. The results indicate that an interaction between palytoxin and Na, K-ATPase leads to opening of a 10-pS ion channel. They further raise the possibility that a channel structure may exist in the sodium pump which is uncovered by the action of palytoxin.
TL;DR: These data provide the first experimental evidence for the view that functional coupling of the ATPase domain of an ABC transporter to the membrane-integral domains is crucial for conferring sensitivity to vanadate and bafilomycin A1.
TL;DR: The results support the view that insulin receptor is one of the sites involved in the insulin-mimetic actions of vanadate, and increases the activities of lipogenic enzymes in streptozotocin-induced diabetic animals and prevents the elevation of activities of these enzymes in hyperinsulinemic animals.
Abstract: The insulin-mimetic action of vanadate is well established but the exact mechanism by which it exerts this effect is still not clearly understood. The role of insulin in the regulation of hepatic glycogen metabolizing and lipogenic enzymes is well known. In our study, we have, therefore, examined the effects of vanadate on these hepatic enzymes using four different models of diabetic and insulin-resistant animals. Vanadate normalized the blood glucose levels in all animal models. In streptozotocin-induced diabetic rats, the amount of liver glycogen and the activities of the active-form of glycogen synthase, both active and inactive-forms of phosphorylase, and lipogenic enzymes like glucose 6-phosphate dehydrogenase and malic enzyme were decreased and vanadate treatment normalized all of these to near normal levels. The other three animal models (db/db mouse, sucrose-fed rats and fa/fa obese Zucker rats) were characterized by hyperinsulinemia, hypertriglyceridemia, increases in activities of lipogenic enzymes, and marginal changes in glycogen metabolizing enzymes. Vanadate treatment brought all of these values towards normal levels. It should be noted that vanadate shows differential effects in the modulation of lipogenic enzymes activities in type I and type II diabetic animals. It increases the activities of lipogenic enzymes in streptozotocin-induced diabetic animals and prevents the elevation of activities of these enzymes in hyperinsulinemic animals. The insulin-stimulated phosphorylation of insulin receptor β subunit and its tyrosine kinase activity was increased in streptozotocin-induced diabetic rats after treatment with vanadate. Our results support the view that insulin receptor is one of the sites involved in the insulin-mimetic actions of vanadate.
TL;DR: The plasma membrane ATPase on the human umbilical vein endothelial cell line (ECV304) was demonstrated to be an ecto-enzyme and identification of compounds that inhibit ATP degradation would prove to be useful to overcome this problem and would lead to the development of invaluable pharmacological tools in many other aspects of purine research.
Journal Article•
TL;DR: Findings show that vanadate triggers activity of this receptor, which in turn stimulates protein tyrosine phosphorylation and induces cell proliferation, which is the first evidence of in vivo association between estradiol receptor tyrosin phosphorylated and its hormone-binding activation.
Abstract: Vanadate stimulates growth of the estradiol-responsive MCF-7 cells in the absence of estrogens through a mechanism requiring tyrosine kinase activity. The proliferative effect of vanadate is mediated by estradiol receptor, and is inhibited by three antiestrogens, hydroxytamoxifen, ICI 164,384, and ICI 182,780. Estradiol abolishes the inhibitory effect of ICI 164,384 or ICI 182,780. Before stimulating cell proliferation, vanadate induces accumulation of tyrosine phosphorylation in several proteins including estradiol receptor and epidermal growth factor receptor. In addition, vanadate increases the binding activity of the estradiol receptor for its ligand. This is the first evidence of in vivo association between estradiol receptor tyrosine phosphorylation and its hormone-binding activation. Antiestrogens abolish the vanadate effect on estradiol receptor and epidermal growth factor receptor phosphorylation and reduce it on general protein tyrosine phosphorylation. These findings show that vanadate, apparently through estradiol receptor tyrosine phosphorylation, triggers activity of this receptor, which in turn stimulates protein tyrosine phosphorylation and induces cell proliferation.